Inhibition of DcR2 and DR5 protein expression by siRNA sensitizes LNCaP cells to TRAIL-induced apoptosis in medium containing 0.1 nM R1881. LNCaP cells, untransfected (Ct: control) or transfected with scrambled siRNA (si0) or siDcR2 or siDR5 (0.5 μg) for 48 h were treated with TRAIL (100 ng/ml) for 24 h (A). White arrows show fragmented nuclei detected by the DAPI method. Histograms represent the number of fragmented nuclei per 1,000 cells from 5,000 randomly selected cells per culture. The values represent the mean ± SD determined from triplicate cultures of a representative experiment from 3 independent experiments. a, P < 0.005, *P < 0.005 and **P < 0.005 versus the other treatment conditions. TRAIL-induced apoptosis, under previous conditions, was controlled by caspase-3 activity assay (B). Histogram values represent the mean ± SD determined from triplicate cultures of a representative experiment from 2 independent experiments performed at 0.1 nM R1881, *P < 0.005 versus the other treatment conditions.